1. Field of the Invention
The present invention relates to a method of manufacturing flexible transparent polyvinyl chloride film without facial flow marks and pits to upgrade the quality of the plastic film (sheet).
2. Description of the Prior Art
In conventional manufacturing process for clear polyvinyl chloride plastic film (sheet), raw material is sufficiently processed and become fully melted state by having it through a mixer, a high speed mixer, a roller machine, and an extruder for working operation so that the melted plastic material after fed and passed to a calender is capably further formed as a film (sheet) material with a desired thickness. Continuously, the film (sheet) material formed is worked by passing a take off roller set with multiple heated or cooled rollers and a cooling roller set internally supplied with cold water to make it filly formation before to be wound into rolls as a finished product.
But, the plastic film (sheet) manufactured from the above conventional method is still existed with the following drawbacks:
(1) The high-temperature melted plastic material is gradually cooled to room temperature during the manufacturing process. During this cooling process, the half-set plastic material is subjected to considerable stretch while its molecules have gradually lost their fluidity. As a result, linear streaks are formed on the surface of the plastic film (sheet).
(2) When winding the plastic film at high speed, a considerable amount of air is brought into the roll between every two adjacent layers of the plastic film (sheet). The air converges to form bubbles widely spreading between the layers, producing pits on the surface of the plastic film (sheet).
The primary object of the present invention is to provide a method of manufacturing flexible transparent polyvinyl chloride film without facial flow marks and pits to upgrade the quality of the plastic film (sheet).
The method according to the present invention mainly includes following steps:
1. Preparing softened and melted PVC material;
2. Feeding the melted plastic material into calender, so that the material is gradually calendered to be a (sheet) having a desired thickness;
3. Sending the film (sheet) material into a water bath tank having a water temperature between 20xc2x0 C. and 85xc2x0 C. to chill and set the material quickly, so that the polyvinyl chloride is partially crystallized to create good transparency, and the melted plastic material instantaneously forms a uniform and stable flexible film (sheet) without facial flow marks;
4. Sending the cooled flexible plastic film (sheet) to pass a water removing equipment in which more than one soft rubber roller and metal roller cooperate with other supplemental water removing means, such as scrappers, air knives, and vacuum suckers, to remove water attached to the surface of the plastic film (sheet) coming out of the bath tank;
5. Sending the plastic film (sheet) coming out of the water removing equipment to pass a series of heating rollers coated with water-absorbent material; heating the plastic film to a temperature from about 40xc2x0 C. to about 150xc2x0 C. to remove residual water and stress from the plastic film (sheet) then control the plastic film (sheet) to a temperature from about 30xc2x0 C. to about 85xc2x0 C.;
6. Winding up the plastic film (sheet) into rolls and applying a pressure from about 1 kg/cm2 to 8 kg/cm2 on the surface of the wound plastic film (sheet) to prevent air to be trapped from forming air bubbles, this film (sheet) with very smooth surface can be produced. If the film (sheet) is wound up by conventional method, usually air bubbles or pit should form on the surface of the plastic film (sheet) due to air captured between two layers of the plastic film (sheet) for a prolonged time.